1. Field of the Invention
The present invention relates to a piston device for internal combustion engines containing compression rings capable of reducing oil consumption during driving at high-speeds and high loads and driving under high-boost conditions.
2. Description of the Related Art
To reduce oil consumption during driving at high-speeds and high-loads and driving under high-boost conditions, the Japanese unexamined utility model application publication No. 5-030624 proposes a compression ring for internal combustion engines. The gap between the both ends of the second compression ring is reduced to the utmost to an extent where the ring ends barely avoid coming in contact, and a notch extending from the outer circumference to the inner circumference is formed on the lower surface of at least one of the ends of the second compression ring, and the gap between the ring ends at the notch on the second compression ring is formed larger than the gap between the both ends of the first compression ring. The Japanese unexamined patent application publication No. 48-21014 proposes a pin 12 provided on the piston 1 for preventing rotation of the ring, and a pair of piston rings 3, 4 including arc-shaped notches formed on the lower surface of the ring ends so as not to interfere with the pin 12. The ring 3 is formed as an undercut ring.
However, on the rings disclosed in the Japanese unexamined utility model application publication No. 5-030624 and Japanese unexamined patent application publication No. 48-21014, the outer circumferential surfaces are both formed as an axial parallel surface so that oil consumption during driving at high-speeds and high-loads and driving under high-boost conditions is still not always satisfactory. The ring disclosed in the Japanese unexamined patent application publication No. 48-21014 contains an arc-shaped notch formed on the lower surface of the ring end so that oil tends to rise upward along the arc-shaped surface.